1. Field of the Invention
The present invention relates to a device for conveying fluid pressures to a differential pressure transducer. This device comprises a single flange. A further improvement incorporates a three way valve manifold integral in the single flange.
2. Description of the Prior Art
In the prior art, differential pressure transmitters are disclosed. Typically a differential pressure transmitter consists of three functional sub groups: flanges, a transducer, and an input/output unit. To sense differential pressure, the transmitter compares two fluid pressures. The fluid pressures are separately conveyed to the transducer by two flanges, mounted on opposite sides of the transducer. Each flange is connected to an impulse piping leg which in turn is connected to a conduit containing fluid under pressure. Each flange is typically separately cast or machined from stainless steel. Where the fluid presents a rigorous corrosive environment, they are constructed of more costly materials, including alloys sold under the trademarks Monel and Hastelloy. The transducer has two separate oppositely facing portions, each of which is affected by one of the two fluid pressures and in response generates an input signal representative of the differential in such pressures. This signal is sent to the input/output unit. The input/output unit functions to power the transducer, to receive the differential pressure input signal from the transducer, to transform the input signal into an industry standardized signal representative of differential pressure and to output that standardized signal for use external to the differential pressure transmitter. A typical prior art transmitter is detailed in product literature of Rosemount Inc., Eden Prairie, MN, the assignee of this application, describing their Model 1151 Differential Pressure Transmitter.
A three valve manifold has frequently been used with a differential pressure transmitter. It has typically been interposed between the conduit and the flanges of the differential pressure transmitter by plumbing it directly to the impulse piping and bolting it to each of the flanges, utilizing o-rings to effect the seal therebetween. Alternatively, the three valve manifold has been installed by similarly plumbing it directly to the impulse piping but interposing short additional sections of impulse piping between the manifold and each of the flanges.
The three valve manifold is used to typically perform three functions: (1) to selectively admit fluid pressure from both impulse piping legs to affect the transducer, (2) to exclude fluid pressure from one impulse piping leg while admitting fluid pressure from the other impulse piping leg to affect both portions of the transducer, and (3) to isolate the transducer completely from the fluid pressure from both impulse piping legs. A typical prior art three valve manifold is detailed in the product literature of Anderson, Greenwood & Co. of Houston, Tex., entitled AGCO Manifolds, Catalog 3000, Revised October 1980.
It is desirable to provide the above listed fluid pressure conveying functions both at reduced cost and with increased safety. This invention provides a single flange that performs the same function as the two flanges previously did. A further refinement incorporates a three valve manifold integral to the single flange. This combination performs the same function as the separate three valve manifold plus the two flanges, which were required prior to this invention. The result in both cases is a functional cost savings due to the invention.
Also important is the aspect of increased safety. It is recognized that the impulse piping conveys whatever process fluid is flowing in the conduit. This fluid may be at high pressure and/or temperature. Likewise, it may be caustic, acidic, flammable or noxious. As such, it constitutes a distinct hazard. In order to minimize this hazard, it is desirable to minimize the number of fluid connections associated with a differential pressure transmitter, as such connections are potential sources of dangerous leakage. Prior to this invention, the minimum number of such connections providing functional equivalence to the single flange with integral three valve mainfold was six; two from the impulse piping to the three valve manifold, two to the flanges and two to the transducer. This invention reduces the number of connections to four; two from the impulse piping to the flange with integral three valve manifold and two from such flange to the transducer.